This invention relates to a process for the preparation of .alpha.-hydroxylated ketones from ketones using a tetrahalogenomethane and alkali metal hydroxide under phase-transfer conditions.
The .alpha.-Hydroxylated ketones preparable by the process of this invention are useful as initiators for the photopolymerization of unsaturated compounds, as described in, for example, German Patent Specification No. 2,722,264. All the products of this invention can be used in accordance with that disclosure and its U.S. equivalents U.S. Pat. Nos. 4,347,111 and 4,477,681, which disclosures are incorporated by reference herein.
A number of processes for the preparation of .alpha.-hydroxylated ketones has been disclosed. A review can be found in Houben-Weyl, Methoden der Organischen Chemie (Methods of Organic Chemistry) published by George Thieme, Stuttgart, vol. VII/2c and in the abovementioned patent specification.
The processes hitherto disclosed have a number of disadvantages. Thus, for example, using chlorine or bromine, ketones of the formula II are converted into the corresponding .alpha.-halogeno ketones. The latter can be reacted with metal alcoholates to give .alpha.-alkoxy epoxides, whose hydrolysis provides the desired .alpha.-hydroxylated ketones of the formula I. However, the resulting wide variety of by-products reduces the yield of desired product.
Under basic conditions .alpha.-halogeno ketones can be hydrolyzed directly to .alpha.-hydroxylated ketones. The latter often suffer base-catalyzed isomerizations or Favorsky rearrangements. The resultant by-products likewise lead to reductions in yield and decreases in the quality of the products of the process.
A process for the preparation of .alpha.-hydroxylated ketones is disclosed in European Published Specification No. 094,347. .alpha.-halogeno ketones are reacted with compounds which generate hydroxide ions in the presence of a phase-transfer catalyst. The requisite halogeno ketones must previously be prepared in an additional process step from the ketones of the formula II. In addition to an increase in the work and costs expended, because substituents on the starting compounds are intolerant of the reaction conditions, the preparation of the .alpha.-halogeno ketones is, frequently associated with by-product formation and the reduction in yield resulting from this.
V. M. Kolb, in a dissertation at Southern Illinois University, Carbondale, 1976, describes a process for the direct .alpha.-hydroxylation of ketones by reaction with carbon tetrachloride and powdered potassium hydroxide in tert-butanol as solvent. In addition to providing yields which mostly are only moderate, hydroxy ketones of the formula I readily suffer rearrangement under the reaction conditions described. Thus, 3,3,6,6-tetramethyl-1,4-diphenyl-2,5,7-trioxabicyclo-[2.2.1] heptane, formed via the intermediate cis-2,2,5,5-tetramethyl-3,6- dihydroxy- 3,6-diphenyl-1,4-dioxane with elimination of water, is isolated in place of 1-phenyl-2-hydroxy-2-methyl-1-propanone. An additional disadvantage is the necessary restriction to the use of powdered, and thus costly and difficult-to-handle, potassium hydroxide as the compound generating hydroxide ions.